a. Field of the Invention
This invention relates to shaped articles having high surface hardness and a method of making such shaped articles. The shaped articles of the present invention can be used in various fields of application including, for example, the fields of architecture, automobile industry and optics.
b. Description of the Prior Art
Synthetic resin shaped articles made of polymethyl methacrylate resin, polycarbonate resins, diethylene glycol bisallyl carbonate resin and the like are lighter in weight and less expensive than glass products. Owing to these advantages, they are used in a wide variety of applications.
However, since such synthetic resin shaped articles have insufficient surface hardness, their surfaces are easily damaged by contact with other objects, impacts, scratches and the like, resulting in a reduced product yield and a spoiled appearance. Especially where these shaped articles are used as optical lenses, fashion glasses, sunglasses, spectacle lenses (such as correcting lenses), windowpanes and the like, any damage caused to the surfaces thereof diminishes their commercial value and/or makes them unusable in a short period of time. Accordingly, it is strongly demanded to improve the surface hardness of such synthetic resin shaped articles. In order to meet this demand, various attempts have heretofore been made.
In Japanese Patent Publication Nos. 39691/'77, 5554/'87, 157865/'83, 35675/'88, 36349/'88 and 45094/'91, the abrasion resistance of shaped articles are improved by coating them with a coating composition containing a mixture of colloidal silica and a hydrolyzable silicon compound.
In Japanese Patent Publication No. 53701/'85, the abrasion resistance and weather resistance of polycarbonate substrates are improved by forming a thermosetting acrylic polymer layer (primer layer) containing an ultraviolet light absorber on the polycarbonate substrates and then forming thereon a coating layer comprising a mixture of colloidal silica and a hydrolyzable silicon compound.
However, the coating layers disclosed in Japanese Patent Publication Nos. 39691/'77, 5554/'87, 157865/'83, 35675/'88, 36349/'88 and 45094/'91 have the following disadvantages. (1) When they are subjected to a Taber abrasion test according to ASTM D-1044 in which a CS-17 truck wheel is used under a load of 250 g and rotated 5,000 cycles, all of them show a haze of as high as 10 to 50%. Thus, their abrasion resistance is much lower than that of glass plates which show a haze of about 3%. (2) Since the adhesion of the coating layer to the substrate is obtained by dissolving the substrate with a specific solvent, usable substrates are limited by the type of solvent used. (3) The adhesion of the coating layer to the substrate is insufficient. More specifically, the adhesion of the coating layer to the substrate is reduced when the coating layer is subjected to a durability test for a long period of time. Moreover, the structure disclosed in Japanese Patent Publication No. 53701/'85 has the disadvantage that, if the primer layer contains a large amount of ultraviolet light absorber, the adhesion of the primer layer to the substrate is reduced.